1. Field of the Invention
The present invention relates to a sheet conveyance control performed in an image forming system, which includes an image forming apparatus (e.g., copying machine, laser beam printer, etc.) and a post-processing apparatus that performs post-processing on sheets discharged from the image forming apparatus.
2. Description of the Related Art
Print On Demand is a prospective technology and business process that can use advanced digital copying machines and relevant printing devices. To realize an image forming system suitable for the Print On Demand, a copying machine is arranged to be connectable with a plurality of large-capacity sheet feeding decks so that various types and different materials of sheets can be used and the sheet feeding operation can be continuously performed for a long time.
In general, an image forming apparatus is connected to a post-processing apparatus that performs insert processing for inserting cover/interleaf to a plurality of sheets output from an image forming apparatus. Furthermore, the image forming apparatus is connected to a plurality of post-processing apparatuses that perform staple processing, punching processing, bookbinding processing, stack processing, and other post-processing.
As discussed in Japanese Patent Application Laid-Open No. 2-147560, a conventional system detects a fully stacked condition of a discharge tray while sheets are discharged to the discharge tray. If the system detects a fully stacked condition of the discharge tray, the system switches the destination of discharged sheets to another discharge tray.
As discussed in Japanese Patent Application Laid-Open No. 11-116134, a conventional system continues stacking discharged sheets for a predetermined time after detection of a fully stacked condition of a discharge tray and then stops the operation performed by a post-processing apparatus.
However, if an image forming system includes a plurality of apparatuses, the length of a sheet conveyance path in the system is variable depending on the arrangement of respective apparatuses to be connected. Accordingly, as illustrated in FIGS. 11 and 12, the maximum number of sheets existing in a conveyance path extending from a sheet feeding unit of an image forming system to a sheet discharge portion of a post-processing apparatus during an image forming operation (hereinafter, referred to as “maximum number of sheets”) is variable depending on the system arrangement.
However, according to the conventional system discussed in Japanese Patent Application Laid-Open No. 2-147560 or Japanese Patent Application Laid-Open No. 11-116134, the maximum number of sheets in the sheet conveyance path that may change depending on the system arrangement is not taken into consideration.
For example, according to a system arrangement illustrated in FIG. 11 including only a finisher and an image forming apparatus, all of sheets S (indicated by bold segments in FIG. 11) existing in a conveyance path can be discharged to a discharge tray even if the image forming apparatus stops image formation processing after detection of a fully stacked condition of the discharge tray. However, according to a system arrangement illustrated in FIG. 12 including a large-scale image forming system, all of sheets S existing in a conveyance path may not be completely discharged to a discharge tray after detection of a fully stacked condition of the discharge tray.
As described above, the number of sheets received by a finisher after detection of a fully stacked condition of a discharge tray is variable depending on the arrangement of respective apparatuses positioned at the upstream side of the finisher.
Therefore, a post-processing apparatus connected to a large-scale image forming system illustrated in FIG. 12 is required to surely receive all the sheets existing in a conveyance path after a fully stacked condition of a discharge tray is detected.
However, if the maximized arrangement of a system is taken into consideration, a small value is set as the number of sheets that identifies a fully stacked condition of the discharge tray. In this case, the determined number of stackable sheets is too small for another arrangement of the system which is not the maximized arrangement.
Furthermore, if the number of sheets that a post-processing apparatus can receive after detection of a fully stacked condition is set to a value comparable to the maximum number of sheets that can remain in a conveyance path, the scale and the cost of the system increase. Furthermore, when the current maximized arrangement is taken into consideration, the arrangement of a discharge tray applicable to the present system will be no longer effective for scale expansion of the system in the future.
Moreover, if the arrangement of an apparatus is determined considering the maximized system, it becomes an over-designed system and does not suit for a minimized system including only an image forming apparatus and a post-processing apparatus.